1. Field of the Invention
The present invention relates to semiconductor integrated circuits, methods for manufacturing semiconductor integrated circuits, electrooptic devices, and electronic devices. More specifically, the present invention relates to a method for transferring a semiconductor element onto an object having material properties different from those of the semiconductor element, such as a substrate.
2. Description of Related Art
Techniques relating to the formation of a semiconductor element on a substrate, which has material properties different from those of the semiconductor element, have been proposed in the field. Such techniques include, for instance, formation of a vertical cavity surface emitting laserdiode (VCSEL), a photodiode (PD), or a high electron mobility transistor (HEMT) on a silicon semiconductor substrate, and attachment of a micro-silicon transistor, instead of a thin film transistor (TFT) of each pixel of a liquid crystal display (LCD), onto a glass substrate.
Examples of the integrated circuits including such a semiconductor having different material properties include an optoelectronic integrated circuit (OEIC). The optoelectronic integrated circuit is an integrated circuit having an optical input/output means. Signal processing in the OEIC is electrically performed whereas light is used for input and output processes of the OEIC.
On the other hand, CPU internal operation speed (internal clocks) in computers has been improved each year due to progress in fine pitch connection in the internal structure of an integrated circuit. However, the improvements in signal transmittance rate in a bus has nearly reached its limit, and this has become a bottle neck in improving the processing rate of a computer. If the signal transmission can be performed using an optical signal in the bus, it becomes possible to significantly improve the limit on the processing rate of a computer. In order to realize this, it is necessary to integrate minute light emitting/detecting diodes into an integrated circuit made of silicon.
However, since silicon is an indirect transition semiconductor, it cannot emit light by itself. Accordingly, it is necessary to form an integrated circuit by combining silicon with another semiconductor light emitting diode.
The VCSEL made from a GaAs compound semiconductor, etc., may be favorably used as a semiconductor light emitting diode. However, it is extremely difficult to directly form the VCSEL on a silicon integrated circuit using a semiconductor process, such as epitaxy, since the VCSEL does not match the lattice structure of silicon.
In general, the VCSEL is formed on a GaAs substrate. Thus, a method has been considered in which an electric signal transmission circuit is merged with an optical signal transmission circuit by making the VCSEL on the GaAs substrate into a chip and mechanically mounting the chip on a silicon integrated circuit substrate.
On the other hand, it is preferable that the size of the VCSEL chip on an integrated circuit be as small as possible from the viewpoint of effectively using the surface of the semiconductor substrate on which the integrated circuit is formed, and of readiness in handling the chip after joining. It is ideal for the size of the chip to be about the same size as a monolithic integrated circuit, i.e., dimensions of a few μm in thickness x a few tens of μm2 in surface area. However, according to convention semiconductor mounting techniques, the size of a chip that can be handled is greater than a few tens of μm in thickness x a few hundreds of μm2 in surface area.
In relation to the above, there are techniques described in “Electronics”, pp. 37-40, (October, 2000) and in “Denshi Joho Tsushin Gakkai Ronbunn-shi (The Institute of Electronics, Information and Communication Engineers Journal), 2001/9, Vol. J84-C No. 9. In the techniques described in the above publications, a substrate is removed by abrasion, and only a functional layer (a few μm thick) of an extreme surface layer, which becomes a semiconductor element, is transferred onto another supporting substrate. Then, the functional layer is formed into a desired size using handling and photolithography techniques, and is joined to a final substrate. In this manner, a semiconductor layer (a functional layer) a few μm thick, which becomes a target semiconductor element, is formed on a desired position of the final substrate. This is processed using a normal semiconductor process, and is made into a product by attaching electrodes, etc.
Problems associated with the conventional techniques described in the above publications include that a supporting substrate of a rigid body becomes necessary since the semiconductor substrate is removed by abrasion. For this reason, it becomes necessary to carry out the joining process to the final substrate at one time for the whole surface. That is, semiconductor membranes at all portions other than the portions that become finally necessary must be removed prior to the joining process. Accordingly, a number of steps become necessary and the process becomes complicated. Also, since the portion that is joined is mere a functional layer, it is necessary to perform a semiconductor process after the joining process. Therefore, a number of steps become necessary for treating the final substrate one by one, especially when the arrangement of target semiconductor elements is not very dense.